Most screw-bolts that secure structural units to vehicle frames in the chassis area are loaded by thrust (shear) parallel to the contact surface between the frame portion and the structural unit connected thereto, and therefore transversely to the axis of the bolt. Typically during braking or acceleration large forces are produced in the longitudinal direction of the vehicle, which in the case of longitudinally positioned contact surfaces bolted together act upon the bolts there in a shearing direction, since the bolts pass through the contact surfaces perpendicularly. With such screw joints, at the contact surfaces only around 10% of the screw force applied can be converted into shear force. However, this pre-stressing normal force prevents the components held together along the contact surface from moving relative to one another in a direction in the plane of the contact surfaces. It is therefore important to ensure a sufficiently large normal force. A large number of screws are needed in order to transmit large forces.
But since the friction coefficients at the contact surfaces vary markedly (according to the literature by a factor of three), such connections have to be made oversized in order to reliably prevent loosening and shearing of the joint even when a large force is applied transversely to the axis of the connecting means. This entails higher material costs and additional weight of the components. However, for the desired lightweight designs and because of the need for more compact fitting spaces, screw joints have to be optimized in relation to weight and size.